Use of circuit breakers is widespread in modern-day residential, commercial and industrial electric systems, and they constitute an indispensable component of such systems toward providing protection against over-current conditions. Various circuit breaker mechanisms have evolved and have been perfected over time on the basis of application-specific factors such as current capacity, response time, and the type of reset (manual or remote) function desired of the breaker.
A circuit breaker employs a pair of mating contacts which establish a current path therebetween during normal operation of the circuit into which the breaker is installed. In response to a high current condition in the circuit, however, the mating contacts separate one another to interrupt the current path therebetween. One of the contacts is a movable contact connected to the end of an elongated rotatable blade, while the other of the contacts is a stationary contact attached to a fixed blow-off terminal. In response to the high current condition, the blow-off terminal provides an electromagnetic repulsion toward the rotatable blade. In one type of blow-off terminal, shown in FIG. 1, a blow-off terminal 10 is configured in the form of a U-shaped loop. The current flow in the blow-off terminal 10 is depicted by the arrows in FIG. 1. It can be seen that the current flow reverses directions in passing from the input section 12 to the output section 14 of the terminal 10. This current reversal causes an electromagnetic repulsion between the input and output sections 12, 14. During normal circuit operation, the current flow from the output section 14 passes through the stationary contact 16 to a mating movable contact (not shown) of a rotatable blade. During a high current condition, the terminal 10 repels the rotatable blade to separate the movable contact from the stationary contact 16. This separation is accelerated by the U-shaped configuration of the blow-off terminal 10.
A drawback of the blow-off terminal 10 is that it is not conducive to manufacturing. In one manufacturing technique, the terminal 10 is fabricated by imparting successive bends perpendicular to the developed length of the raw metal material used for its fabrication. In FIG. 1, these bends are designated by the reference numerals 18 and 20. While this process economizes material usage, the forming process becomes more difficult with each subsequent bend. The manufacturer must accommodate brazing operations either by partially forming the terminal with the bend 18, and then proceed to either braze the contact 16 to the output section 14 or at least provide some kind of clearance holes so that the contact 16 can later be attached to the output section 14. The terminal 10 must then have a final forming operation where the bend 20 is imparted thereto. This final forming operation is difficult to perform because the contact 16 is already in place and because the terminal material has been partially annealed from the brazing operation.
In another manufacturing technique, the terminal 10 is formed from two or more separate pieces which are either mechanically fastened or welded together. Drawbacks of this technique are that it is part intensive and it can be a source of high resistance within the assembled terminal.
Accordingly, there is a need for a blow-off terminal which can be implemented without the aforementioned shortcomings.